The Mexican American War Facts, Worksheets, Causes & Key Events

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The Mexican American War was an armed conflict between the United States and Mexico in the years 1846 to 1848. It is known as the “Mexican War” in the United States and as “U.S. intervention in Mexico” (Intervención Estadounidense en México) in Mexico.

In 1718, San Antonia was the first settlement to be established in Texas by Spanish missionaries. The area remained sparsely populated due to its vastness and hostility from Native American tribes.
In 1810, Mexico won the War for Independence from Spain. Led by Father Miguel Hidalgo y Costilla, it ratified a progressive Constitution in 1824 that established a federal government with considerable powers given to the states.

The Mexican government allowed American settlers to claim land in the Texas region as colonists, after taking an oath of allegiance and converting to Catholicism.
Thousands of Americans accepted the invitation, resulting in a population explosion and, over time, the number of Mexicans of Spanish descent was higher than that of Americans.
The new settlers were not satisfied with the way the Mexican government was managing the territory, however, and so there was a struggle for independence with a unity of purpose for both the Americans and Mexicans living in the area.
In 1835 there was a revolution that led to the Independence of Texas from Mexico, with Sam Houston as President. The Mexican President Santa Anna was captured and forced to sign the Treaty of Velasco.
The Republic of Texas was unable to permanently defend itself against Mexican troops and decided to negotiate with the U.S. to join the Union in 1845.
The Manifest Destiny, the belief that America was specially ordained by God to spread the influence of its democracy and institutions to uncivilised people on the continent, was the main force behind the Mexican American war.
President Polk offered to buy the southwest land from Mexico, but Mexico declined, causing tensions that contributed to the war.
Mexico was not happy with Texas joining the Union and also disagreed with the U.S. on the border. Mexico placed the border at the Nueces River while Texas claimed the border was further south at the Rio Grande River.

President Polk sent troops to protect the Texas border, where they met the Mexican forces and a shouting brawl ensued. On 7 July 1846, the U.S. declared war on Mexico.
The Mexican army was led by Santa Anna and the U.S. forces by General Zachary Taylor. They fought at Palo Alto where the Mexicans were forced to retreat.
President Polk then told the U.S. congress “the cup of forbearance has been exhausted, even before Mexico passed the boundary of the United States, invaded our territory, and shed American blood upon American soil.”
On May 13, congress officially declared war, despite the opposition of some Northern lawmakers. However, Mexico never stated their official declaration of war.
The United States entered the war despite some oppositions. Most of the Whig Party saw the president’s motive as conscienceless land invading. Whigs in the Senate and House challenged the honesty of the assertion by Polk that the initial conflict happened in U.S. territory.
President Polk then accused the Whigs of treason in December 1846. A month later, Whigs in the House voted to reprimand the Polk for “a war unnecessarily and unconstitutionally begun by the President of the United States.”
General Antonio López de Santa Anna contacted Polk when the war broke out. President Polk arranged a ship for Santa Anna for the purpose of working for peace. However Santa Anna took charge of the Mexican forces instead of acting for peace.

General Taylor advanced into Mexico, fighting at the city of Monterrey and a mountain pass called Buena Vista. In the battle at Buena Vista, Taylor’s 5,000 troops defeated Santa Anna’s 14,000 men.
President Polk did not trust General Taylor and instead of replenishing his troops to capture Mexico City, he sent General Winfield Scott who captured it in August 1847. Santa Anna made one last attempt to defeat the U.S. Army in late September 1847, by cutting them off from the coast. The fall of the Mexican capital ended the military phase of the conflict.

The Mexicans were forced to concede defeat and agree to a treaty called the Treaty of Guadalupe Hidalgo on February 2, 1848.
In the settlement, Mexico agreed to border Texas at the Rio Grande and sold 55% of its land to the U.S. at 15 million dollars.
Presently this land makes up the states of California, Nevada, Utah, Arizona and parts of Wyoming, Oklahoma, New Mexico, and Colorado.
The U.S. victory brought a surge of patriotism. It seemed to fulfil the belief of democrats in the Manifest Destiny of their country.
The Mexican American War also marked a significant turning point for the U.S. as a growing military power.
Despite the opposition of the Whigs, they praised the military performance of Zachary Taylor and made him their presidential candidate. Taylor became known as a national hero and succeeded James Polk as president in 1849.

During the U.S. invasion in Mexico, the U.S. Army attacked a Military Academy at Chapultepec Castle in Mexico City. Six Mexican students died defending the castle. They are remembered as the Niños Heroes (boy heroes) in Mexico with a national holiday on 13 September.
The Mexican government established the National Museum of Interventions (Museo Nacional de las Intervenciones) in a former convent that was the location of the Battle of Churubusco.
The museum includes exhibits showing the Spanish attempts to reconquer Mexico after its independence.

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